按柴胡为少阳药者，因伤寒少阳证之用柴胡汤也。夫邪入少阳，将有表邪渐解，里邪渐着之势，方以柴、芩对峙，
解表清里的为少阳和解之法。而柴胡实未印定少阳药也，盖以柴胡之性苦平微寒，味薄气升，与少阳半表之邪适合其用
耳。乃有病在太阳，服之太早，则引贼入门；若病入阴经，复服柴胡，则重虚其表之说，此恐后人误以半表半里之品，
为认病未清者，模糊混用，故设此二端以晓之也。不观之景岳《新方》中诸柴胡饮、柴芩煎、柴胡白虎煎诸方，信手拈
用，头头是道，是诚知柴胡之用，而先得我心之所同然矣。再古方中有逍遥散之疏解郁热，归柴饮之和营散邪，补中益
气汤之升发清阳，提邪下陷，疏肝益肾汤之疏肝清热，养阴透邪，其妙难于仆数，何至重虚其表乎？余于风邪初感之轻
症，及邪气淹留，表热不解之久病用之，并臻神效，奈何将此有用之良品，拘泥成说而畏之，即用亦准之以分数，竟至
相沿成习，不得不为置辩。
按朱南阳有“如无犀角、以升麻代之”之说，以其同于一透也，朱二允以此二味升降悬殊为辩，余谓尚非确论。夫
犀角乃清透之品，升麻乃升透之味，一重于清，一重于升，其性不同，其用自异，未尝闻有异而可代者也。若夫风寒壅
遏，疹点未透者，斯为升麻之任；而温邪为病，丹斑隐现者，又系犀角之司。如以升麻为代，其肺气热者，必致喉痛，
甚增喘逆；营分热者，必致吐血，轻亦衄宣，其误若此，岂可代乎？又角生于首，故用为透剂，二允以为下降之品，亦
不可不辩，余非敢轻议前辈，实出婆心之不禁耳，故谨论之。
按：柴胡被归为少阳经用药，是因为在伤寒少阳证中使用了以柴胡为主的方剂。邪气侵入少阳，往往呈现出表邪逐渐消退、里邪逐渐加重的趋势，因此方剂中柴胡与黄芩相互对峙（并列使用），通过解表清里的作用，构成了少阳病的和解治法。然而，柴胡实际上并未被固定限定为仅属于少阳经的药物。这是因为柴胡的药性苦平微寒，气味轻薄且主升散，恰好适用于半表半里的病邪罢了。至于那些认为“病在太阳经时过早服用柴胡，会引贼入门户”以及“病入阴经后若再服柴胡，会导致体表更加虚弱”的说法，这恐怕是担心后人将半表半里的药物误用于诊断不清的病症而模糊混用，所以特意设立这两种情况来警示后人。
难道没有看到张景岳《新方》中的各种柴胡饮、柴芩煎、柴胡白虎煎等方剂吗？他信手拈来，运用得当，条理清晰，这确实是深知柴胡的功效，并与我心中所认同的观点不谋而合。再看古方中有逍遥散疏解郁热，归柴饮调和营血疏散邪气，补中益气汤升发清阳、提升下陷之邪气，疏肝益肾汤疏肝清热、滋养阴液透达邪气，其奥妙难以一一列举，怎么会导致体表更加虚弱呢？我在治疗风邪初感引起的轻症，以及邪气滞留、表热不解的久病时，使用柴胡都取得了神效，为何要拘泥于旧说而畏惧使用它呢？即使使用也严格限制剂量，以至于形成了一种习以为常的风气，我不得不为此进行辩驳。
另外，朱南阳有“如果没有犀角，可以用升麻代替”的说法，理由是两者都有透发的作用。朱二允对此提出辩驳，认为这两味药的升降作用相差悬殊。我认为这也不是确切的结论。犀角是清热透邪的药物，升麻是升散透邪的药物，一个侧重于清热，一个侧重于升散，它们的药性不同，功效自然各异，从未听说过性质不同却可以互相替代的。如果是风寒壅滞遏阻，导致疹点未能透发，这是升麻的职责；而温邪致病，出现丹毒斑疹隐隐显现的情况，则是犀角的主管范围。如果用升麻代替犀角，对于肺经有热的患者，必然导致咽喉疼痛，甚至加重气喘逆乱；对于营分有热的患者，必然导致吐血，轻则鼻出血，错误竟然如此严重，怎么可以替代呢？此外，犀角生于头部，因此用作透发之剂，朱二允认为它是下降性质的药物，这一点也不得不辩驳。我不敢轻易议论前辈，实在是出于不忍之心，所以谨慎地论述此事。
Note: Chai Hu (Bupleuri Radix) is classified as a herb for the Shaoyang (Lesser Yang) channel because it is the key ingredient in formulas used for Shaoyang syndrome in cold damage diseases. When pathogenic factors enter the Shaoyang, there is often a trend where exterior pathogens gradually resolve while interior pathogens intensify. Therefore, in such formulas, Chai Hu and Huang Qin (Scutellariae Radix) are juxtaposed to achieve the harmonizing method of Shaoyang by releasing the exterior and clearing the interior. However, Chai Hu has not been strictly fixed as a herb exclusive to the Shaoyang channel. This is because Chai Hu possesses a bitter, neutral, slightly cold nature, with a light flavor and ascending aroma, which aptly suits the treatment of pathogens located at the half-exterior half-interior level.
As for the assertions that "administering Chai Hu too early when the disease is in the Taiyang (Greater Yang) stage will invite the thief into the house" and "if Chai Hu is taken after the disease has entered the Yin channels, it will further deficiency the exterior," these warnings likely stem from concerns that later practitioners might vaguely misuse half-exterior half-interior herbs due to unclear diagnosis. Thus, these two scenarios were established to clarify this point. Have we not observed various formulas in Zhang Jingyue's *New Formulas*, such as various Chai Hu Decoctions, Chai Qin Decoction, and Chai Hu Baihu Decoction? He applied them effortlessly and appropriately, demonstrating a clear understanding of Chai Hu's utility, which aligns perfectly with my own views. Furthermore, ancient formulas include Xiaoyao San (Free and Easy Wanderer Powder) for dispersing constrained heat, Guichai Yin (Angelica and Bupleurum Decoction) for harmonizing Ying (Nutritive) level and dispersing pathogens, Buzhong Yiqi Tang (Tonify the Middle and Augment the Qi Decoction) for raising clear Yang and lifting sinking pathogens, and Shugan Yishen Tang (Soothe Liver and Benefit Kidney Decoction) for soothing the liver, clearing heat, nourishing Yin, and venting pathogens. Their subtleties are numerous and difficult to enumerate; how could they cause further deficiency of the exterior? When I use Chai Hu for mild cases of initial wind-pathogen invasion or for chronic conditions where pathogens linger and exterior heat persists, it yields miraculous effects. Why should one fear this useful, high-quality herb due to rigid adherence to old theories? Even if used, its dosage is strictly limited, leading to a customary practice that I feel compelled to refute.
Regarding Zhu Nanyang's statement that "if Rhinoceros Horn is unavailable, Sheng Ma can be used as a substitute" on the grounds that both have venting properties, Zhu Eryun argued against this, citing the significant difference in their ascending and descending actions. I consider this not to be a definitive conclusion. Rhinoceros Horn (Rhinocerotis Cornu) is a substance for clearing heat and venting pathogens, whereas Sheng Ma (Cimicifugae Rhizoma) is a substance for ascending and venting. One emphasizes clearing heat, while the other emphasizes ascending action; their natures differ, and thus their applications naturally diverge. It has never been heard that substances with different natures can be substituted for one another. If wind-cold is congested and obstructed, preventing the eruption of rashes, this falls under the responsibility of Sheng Ma. Conversely, if warm pathogens cause erythema and macules to appear intermittently, this is governed by Rhinoceros Horn. If Sheng Ma were used as a substitute, patients with lung-heat would inevitably suffer from sore throat, potentially worsening wheezing and counterflow qi. Patients with heat in the Ying (Nutritive) level would inevitably experience hematemesis, or at least epistaxis. Such errors are severe; how can substitution be justified? Moreover, since Rhinoceros Horn grows on the head, it is used as a venting agent. Zhu Eryun's claim that it is a descending substance also requires refutation. I dare not lightly criticize predecessors, but out of sincere concern, I have cautiously discussed this matter.